Photovoltaic cells are used to produce electrical energy from sunlight, offering a green alternative to traditional methods of electricity generation. These solar cells are built from various semiconductor systems which must be protected from environmental effects such as moisture, oxygen, and UV light. The cells are usually jacketed on both sides by encapsulating layers of glass and/or plastic films forming a multilayer structure known as a photovoltaic module. Fluoropolymer films are recognized as an important component in photovoltaic modules due to their excellent strength, weather resistance, UV resistance, and moisture barrier properties. Especially useful in these modules are film composites of fluoropolymer film and polyester film which act as a backing sheet for the module. Such composites have traditionally been produced from preformed films of fluoropolymer, specifically polyvinyl fluoride (PVF), adhered to polyester substrate film, specifically polyethylene terephthalate. When fluoropolymer such as PVF is used as a backing sheet to the module, its properties significantly improve module life, allowing module warranties of up to 25 years. Fluoropolymer backing sheets are frequently employed in the form of laminate with polyethylene terephthalate (PET) films, typically with the PET sandwiched between two fluoropolymer films.
However, laminates of preformed fluoropolymer films on polymeric substrates having a bond which will not delaminate after years of outdoor exposure are difficult to make. Prior art systems such as U.S. Pat. No. 3,133,854 to Simms, U.S. Pat. No. 5,139,878 to Kim et al., and U.S. Pat. No. 6,632,518 to Schmidt et al. describe primers and adhesives for preformed films that will produce durable laminate structures. However, these processes require the application of at least one adhesive layer, or both a primer and adhesive layer, prior to the actual lamination step. The lamination step then requires the application of heat and pressure to form the laminate. Therefore, prior art laminates using preformed fluoropolymer films are expensive to manufacture and/or require capital intensive equipment. Because preformed fluoropolymer films must have sufficient thickness to provide strength for handling during manufacture and subsequent processing, the resulting laminates may also incorporate thick expensive layers of fluoropolymer, i.e., thicker than are necessary for an effective protective layer.